Method and apparatus for heat-treating of workpieces

ABSTRACT

Workpieces are heat treated in an industrial furnace having a horizontally elongated heat-treating chamber. The workpieces to be treated re advanced through the chamber in a path intermediate the top and bottom walls bounding the same. Streams of substantially fully combusted combustion gases are introduced into the chamber from the lateral walls at speeds in excess of 50 m./sec. and with such orientation that they form above and below the workpiece two pairs of laterally adjacent gas spirals each of which rotates about its axis which extends in the direction of elongation of the treating chamber, the direction of rotation being always towards the associated other gas spiral of the pair.

United States Patent inventors Ruediger Knaak Neuss; Richard Sitte,Kleinenbroich, Germany Appl. No. 804,063 Filed Mar. 3, 1969 PatentedJan. 19, I971 Assignee Kopper-Wistra-Ofenbau Gesellschaft mitDuesseldorlJ-leerdt, Germany Priority Mar. 2, 1968 Germany METHOD ANDAPPARATUS FOR HEAT- TREATING OF WORKPIECES 7 Claims, 3 Drawing Figs.

US. Cl 263/6, 263/43 Int. Cl F27b 9/14 Field of Search 263/6, 68,

43. (Recirculation Digest) 3,208,740 9/1965 Nesbittetal PrimaryExaminer-John J. Camby Attorney-Michael S. Stn'ker ABSTRACT: workpiecesare heat treated in an industrial furnace having a horizontallyelongated heat-treating chamber. The workpieces to be treated areadvanced through the chamber in a path intermediate the top and bottomwalls bounding the same. Streams of substantially fully combustedcombustion gases are introduced into the chamber from the lateral wallsat speeds in excess of 50 m./sec. and with such orientation that theyform above and below the workpiece two pairs of laterally adjacent gasspirals each of which rotates about its axis which extends in thedirection of elongation of the treating chamber, the direction ofrotation being always towards the associated other gas spiral of thepair.

METHOD AND APPARATUS FOR HEAT-TREATING OF WORKPIECES BACKGROUND OF THEINVENTION The present invention relates generally to the heat-treatingof workpieces, and more particularly to a method of heattreatingworkpieces in an industrial furnace. The method of the invention alsorelates toan apparatus'for carrying out the method.

In the heat-treating of workpieces in continuously operating industrialfurnaces, the workpieces generally require a very well defined specificvolume of space within the heat-treating chamber. This is different frombatch-type furnaces because there workpieces of different sizes anddifferent quantities of workpieces are usually present in differentbatches, whereas in continuously operating furnaces, workpieces of agiven series have identical dimensions and the quantity of workpieces inthe heat-treating chamber at any given time is usually unvarying.Accordingly, in continuous furnaces of this type the available volumewithin the heat-treating chamber, that is the volume in which the hotgases may move, remains substantially unchanged at all times.

This is important because in the type of heat-treating furnace underdiscussion there is a relatively large volume of space above and, insome instances, also below the workpieces which are advanced through thetreating chamber. The reason for this is to allow for high heat exchangevalues resulting from radiation of the combustion gases which areintroduced into the heat-treating chamber. The manner in which heatingof these volumes of space is effected may vary according to what isknown in the art. It is known to arrange burners in the top wallbounding the heat-treating chamber as well as to arrange them in thelateral walls. A further known expedient is to pro vide so-called burnerbridges which extend transversely of the direction of movement of theworkpieces above or below, and operative for ejecting combustion gasessubstantially in the direction of movement of the workpieces. Both typesof solu tions suffer from some disadvantages. The so-called lateralburners which are arranged in the sidewalls bounding the chamber fail toprovide for uniform heating of the workpieces across the width of thechamber, that is transversely of the direction of movement of theworkpieces. The reason for this is that the conventional burners haverelatively low issue speeds, that is speed at which combustion gasesissue from the burner and enter into the heat-treating chamber, so thatthe rate of admixture of the combusted gases with the ambient atmosphereprevailing in the treating chamber is slow with the result that heatradiation onto the workpiece is uneven. A further disadvantage is thefact that combustion in large measure takes place only after thecombustion gases have entered into the heat-treating chamber; thisresults in the development of flame jets which further intensify theunevenness of heating of the workpieces. In fact, these problems havebeen so pronounced that in the past two decades there has been a decidedmovement away from the use of lateral burner arrangements.

Ceiling burners, on the other hand, require special mountingarrangements and are usable only in the ceiling, that is the upper wallbounding the heat-treating chamber. Furthermore,

the burner. Inasmuch as the intensity of heat radiation onto the surfaceof the workpiece is always dependent upon the thickness of the layer ofcombustion gas in the volume of space adjacent the respective surface,it will be clear that this decrease in space between the respectiveburner banks and the facing surfaces of the work pieces indisadvantageous because it necessitates a decrease in the layer ofcombustion gases which can be located in this space. This iscontradictory to the deliberate attempt to provide in such heat-treatingfurnaces spaces above and/or below the workpieces to be heat treatedwhich are as large as possible to accommodate the maximum thicknesslayer of combustion gases. A further disadvantage of the use of burnerbanks is the fact that the abrupt the use of this type of burnernecessitates the provision of a large number of relatively small burnerswhich evidently increases the expenses involved quite drastically.

The other possibility, that is the arrangement of burners in form ofbridges or banks, makes possible an even heating of the workpiecesacross the width of the chamber. However, the higher the capacity of thefurnace is to be, the higher must be the number of such bridges orburner banks, as they will be called hereafter. This presents a problembecause these banks require rather significant amounts of space toassure access and the possibility of removing and installing burners andauxiliary equipment. This, on the other hand, drastically decreases thevolume of space between the respective burner bank and the facingsurface of the workpiece advancing past changes in the cross section ofthe free space above and/or below the advancing workpiece, which resultfrom the presence of the burner banks, may result in sudden accelerationof the combustion gases sweeping through the interior of the chamber,and the impingement of the thus accelerated combustion gases upon thewalls bounding the chamber, particularly wall projections which arenecessitated in the region of the burner banks, may result in damage tothe walls.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to overcome the aforementioned disadvantages.

A more particular object of the present invention is to provide a methodof heat-treating workpieces in continuously operating industrialfurnaces.

A further object of the invention is to provide such a method which willresult in more even and quicker treating of the workpieces.

Yet a further object of the invention is to provide an apparatus forcarrying out the method. 7

In accordance with the above objects, and others which will becomeapparent hereafter, one feature of our invention resides in theprovision of a method of heat-treating workpieces in an industrialfurnace provided with a horizontally elongated treating chamber havingan. upper and a lower wall. According to our method a workpiece to betreated is advanced through the chamber in a path intermediate thewalls, and streams of substantially fully combusted combustion gases areintroduced into the chamber at speeds in excess of 50 m./sec.Furthermore, the streams of combustion gases are so oriented as to formintermediate the workpiece and at least one of the top and bottom wallsa pair of laterally adjacent gas spirals each of which has an axiscoincident with the direction of elongation of the treating chamber anda rotary component of movement about its respective axis in directiontowards the associated gas spiral.

By resorting to our novel method and utilizing high-speed burners havingejection nozzles of relatively small cross section but ejecting thecombustion gases at high speeds, the

ejected streams of combustion gases are admixed with the ambientatmosphere prevailing in the heat-treating chamber much more rapidlythan has been possible heretofore. This evidently provides fortemperature equalization in the direction of the heating chambertransversely of the advancement of the workpieces, thus eliminating thedisadvantages of heretofore-known lateral burner constructions. Byfurthermore assuring that the combustion gases entering the treatingchamber from the burners are at least substantially fully combustedbefore they so enter, the disadvantageous effects of flame jets areeither eliminated or significantly reduced.

It is, however, the main concept of the invention to so orient theincoming streams of combustion gases that the combustion gases areforced into a spiral movement about an axis or axes coincident with thedirection of advancement of the workpieces, that is the direction ofelongation of the heattreating chamber. In other words, the kineticenergy of the streams of combustion gases is not allowed to becomedissipated, but rather is retained to a significant extent with theresult that the constant spiral movement of the streams of combustiongases effects constant circulation and turnover of the entire ambientatmosphere and eliminates the accumulation of stagnant gas in so-calleddead corners, a phenomenon which evidently results in inadequate heatradiation from such areas and therefore inadequate heat-treating ofworkpiece portions'which are exposed to gases in such areas.

Thel'riovel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a diagrammatic verticaltransverse section illustrating a furnace for carrying out ourinvention, according to one embodiment;

FIG. 2 is a view similar to FIG. I but illustrating a further embodimentof the invention; and

FIG. 3 is a view similar to FIG. 1 but illustrating yet an additionalembodiment of the invention. I

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing firstly FIG. 1 itwill be seen that reference numeral I identifies the lateral walls, andreference numeral 1a identifies the top and bottom walls which togetherbound the heat-treating chamber 1b of a continuously operatingindustrial furnace. It is not believed necessary to discuss furtherdetails concerning the general construction of such a furnace becausethis is conventional and forms no part of the invention.

In the illustrated embodiment guide means 4 are provided locatedsubstantially midway between the top and bottom walls Ia and extendingin what is the direction of elongation of the. heatrtreating chamber,that is intermediate the (nonillustrated) inlet and outlet thereof. Inconventional manner the guide means 4 may be constructed as water-cooledtubular guides. The workpiece or workpieces 3 are advanced resting onthe guide means 4. Thus, in the illustrated embodiment of FIG. I thereis a space between the upper side of the workpiece 3 and the top wall Inand a further space between the lower side of the workpiece 3 and thebottom wall la.

As shown in FIG. I, the sidewalls I are provided with lateral burners 2which are so arranged as to reject streams of combustion gases into theinterior of the heat-treating chamber lb in the direction of therespectively indicated arrows. The burners 2 are of the high-speed typewhich ejects the combustion gases, when in full operation, with anoutlet speed of more than 50 m./sec.; the burners 2 are further soconstructed that the combustion gases are at least substantially fullycombusted before they enter into the heat-treating chamber lb. Burnerssuch as the ones identified with reference numeral 2 in FIG. 1 are wellknown to those skilled in the art and are therefore not described indetail. Their construction does not, in itself, constitute a part of thepresent invention.

As evident from FIG. 1, the burners 2 are arranged in pairs with theburners of each pair being transversely aligned in the opposite lateralwalls 1, and with the combustion gases issuing from the respectiveburners having such an orientation that they form spirals or coils 5 ofwhich in the illustrated embodiment of one pair is located in the spaceabove and one pair is located in the space below the workpiece 3. Wewish it to be understood, however, that the construction of the furnacemay be such that only a space exists above the workpiece, or that aspace exists only below the workpiece. In this case there would then ofcourse be only one pair of the spirals 5. In any case, the spirals areshown to have longitudinal axes which extend in the direction ofelongation of the chamber lb, that is in the direction of advancement ofthe workpiece 3. As indicated by the arrows associated with therespective spirals 5, the combustion gases rotate in such a manner thatthe gases in each spiral rotate towards the other spiral of the pair,that is after the combustion gases issue from the respective burnersthey rotate towards the middle of the chamber and then reverse directionto rotate back towards the sidewall 1 from which they have just issued.Of course, there is a component not only of rotary movement, asillustrated by the arrows, but also a component of longitudinal movementwhich is not shown but which is largest where the component of rotarymovement is smallest, that is at the core or center of the spirals 5 andin the space below the workpiece 3 in the area between the guide members4. I

The embodiment of FIG. 2, which is basically similar to that of FIG. 1and wherein like elements are identified with like reference numerals,we have shown a construction wherein workpieces may be advanced throughthe heat-treating chamber on two or more vertically spaced andsuperimposed levels. The manner in which this is accomplished is thesame as in FIG. I, that is the workpieces 3 advance on guide members 4.Of course, as in the case of FIG. 1 it is immaterial what means areutilized for advancing the workpieces 3 because such means are entirelyconventional and form no part of the invention.

As evident in FIG. 2, there is a space between the upper and lower guidemeans, that is between the upper and lower workpieces, because the guidemeans are vertically spaced from one another. In such a construction theheat requirements, the space requirements and the economic expendituresfor construction of thefurnace are reduced over what would be necessaryfor constructinga requisite number of separate fur naces capable of thesameoutput.

In accordance with the embodiment illustrated in FIG. 2 we provideadditional high-speed burners 6 associated with the respective lateralwalls 1 and transversely aligned, as before. They are arrangedapproximately midway between the upper and lower limits of the spaceexisting' between the upperand lower workpieces and, when in operation,produce two further superimposed pairs of combustion gas spirals, ofwhich the spirals of the upper pair are identified with referencenumeral 5a and those of the lower pair with reference numeral 5b. Itshould be noted, however, that their rotational component is reversedwith respect to the rotational component of the spirals 5. Theadvantages of this construction are the same as discussed above withrespect to FIG. 1 except that in the embodiment of FIG. 2, twoworkpieces, or two layers of workpieces, may be treated simultaneously.Of course, it is possible to further expand the construction of FIG. 2by providing additional layers of workpieces and additional ones of theburners 6.

The type of furnace with which our present invention is utilized maydiffer. Thus, it is possible to use pusher-type furnaces,walkingbeam-type furnaces, roller-hearth-type furnaces or rotary-hearthfurnaces. The arrangement of the burners 2as opposed to the burners 6 ofFIG. 2is advantageously such that they eject their streams of combustiongas into the upper third of the volume of space above the workpieces andinto the lower third of the volume of space below the workpieces, asillustrated in FIG. 1.

Coming, finally, to the embodiment illustrated in FIG. 3, it will beseen that this is largely the same as the one of FIG. 1 from which itdiffers only in the provision of partition walls 7 which extend from therespective top and bottom walls 10 into the chamber lb towards but shortof the guide means 4 so as to subdivide the upper space above theworkpieces 3 and the lower space below the workpieces 3 in the mannerillustrated in FIG. 3. The purpose of these partition walls 7, whichextend in the direction of elongation of the heat-treating chamber Iband therefore in the direction of movement of the workpieces 3, is toenhance, particularly in furnaces having relatively small distancebetween the lateral walls 1 thereof, the direction reversal of theincoming streams of combustion gases to thereby facilitate theirguidance in a sense forming the gas spirals 5.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied inthe heat treatment of workpieces. It is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention. The gas streams issuing from the burners (in FIGS. 1 and 2)are caused to be deflected so as to form the rotating spirals by thefact that the burners are located opposite each other in pairs, with theoppositely directed gas streams mutually deflecting one another.

We claim:

1. A method of heat-treating workpieces in an industrial furnaceprovided with a horizontally elongated treating chamber having an upperand a lower wall, comprising the steps of advancing a workpiece to betreated through said chamber in a path intermediate said walls; andintroducing streams of substantially fully combusted combustion gasesinto said chamber at spaced locations at speeds in excess of 50 m./sec.and with orientation that said gas streams impinge upon one another andform intennediate said workpiece and at least one of said top and bottomwalls a pair of laterally adjacent gas spirals each of which has an axiscoincident with the direction of elongation of said treating chamber anda rotary component of movement about its respective axis in directiontowards the associated gas spiral.

2. A method as defined in claim 1; further comprising the step ofintroducing further streams of said combustion gases into said chamberat said speeds and with such orientation as to form intermediate saidworkpiece and the other of said top and bottom walls a further pair oflaterally adjacent gas spirals similar to the first-mentioned pair.

3. A method as defined in claim 2; further comprising the step ofadvancing an additional workpiece through said chamber in an additionalpath vertically spaced from the firstmentioned path; and introducinginto said chamber additional streams of said gases at speeds in excessof 50 mJsec. and with such orientation as to fonn in the space betweensaid paths two additional superposed pairs of laterally adjacent gasspirals similar to the first-mentioned pairs of gas spirals.

4. An industrial furnace for heat-treating workpieces, comprising wallmeans defining a horizontally elongated treating chamber havingtransversely spaced sidewalls and vertically spaced top and bottomwalls; guide means extending longitudinally of said chamber in a planeintermediate said top and bottom walls for guiding a workpiece foradvancement through said chamber; and burner means includingpairs ofburners provided in said sidewalls transversely aligned for ejectingstreams of substantially fully combusted combustion gases into saidchamber at speeds in excess of 50 m./sec. transversely of the directionof advancement of said workpiece and into the space between saidworkpiece and at least one of said top and bottom walls with suchorientation that said gas streams impinge upon one another in a sensecausing their conversion into respective rotating gas spirals, wherebyto obtain between said workpiece and said one wall a pair of laterallyadjacent gas spirals each of which has an axis coin cident with thedirection of elongation of said chamber and a rotary component ofmovement about its respective axis in direction towards the associatedgas spiral.

5. A furnace as defined in claim 4, said burner means comprising furtherpairs of burners provided in said sidewalls transversely aligned andoperative for ejecting further streams of said combustion gases at saidspeeds into a further space" between said workpiece and the other ofsaid top and bottom walls whereby to provide in said further space afurther pair of laterally adjacent gas spirals similar to thefirst-mentioned pair.

6. A furnace as defined in claim 5, said guide means comrising first andsecond guide instrumentalities for guiding the irst-mentioned workpieceand an additional workpiece in two vertically superposed spaced planes;and said burner means including additional pairs of burners provided insaid sidewalls transversely aligned and operative for ejecting into thespace between said workpieces two additional superposed pairs oflaterally adjacent gas spirals similar to the firstmentioned pairs ofgas spirals.

7. A furnace as defined in claim 5; and further comprising divider meansprovided on said top and bottom wall, respectively, projecting into saidchamber and extending longitudinally of said chamber intermediate therespective gas spirals of each pair of gas spirals.

1. A method of heat-treating workpieces in an industrial furnaceprovided with a horizontally elongated treating chamber having an upperand a lower wall, comprising the steps of advancing a workpiece to betreated through said chamber in a path intermediate said walls; andintroducing streams of substantially fully combusted combustion gasesinto said chamber at spaced locations at speeds in excess of 50 m./sec.and with orientation that said gas streams impinge upon one another andform intermediate said workpiece and at least one of said top and bottomwalls a pair of laterally adjacent gas spirals each of which has an axiscoincident with the direction of elongation of said treating chamber anda rotary component of movement about its respective axis in directiontowards the associated gas spiral.
 2. A method as defined in claim 1;further comprising the step of introducing further streams of saidcombustion gases into said chamber at said speeds and with suchorientation as to form intermediate said workpiece and the other of saidtop and bottom walls a further pair of laterally adjacent gas spiralssimilar to the first-mentioned pair.
 3. A method as defined in claim 2;further comprising the step of advancing an additional workpiece throughsaid chamber in an additional path vertically spaced from thefirst-mentioned path; and introducing into said chamber additionalstreams of said gases at speeds in excess of 50 m./sec. and with suchorientation as to form in the space between Said paths two additionalsuperposed pairs of laterally adjacent gas spirals similar to thefirst-mentioned pairs of gas spirals.
 4. An industrial furnace forheat-treating workpieces, comprising wall means defining a horizontallyelongated treating chamber having transversely spaced sidewalls andvertically spaced top and bottom walls; guide means extendinglongitudinally of said chamber in a plane intermediate said top andbottom walls for guiding a workpiece for advancement through saidchamber; and burner means including pairs of burners provided in saidsidewalls transversely aligned for ejecting streams of substantiallyfully combusted combustion gases into said chamber at speeds in excessof 50 m./sec. transversely of the direction of advancement of saidworkpiece and into the space between said workpiece and at least one ofsaid top and bottom walls with such orientation that said gas streamsimpinge upon one another in a sense causing their conversion intorespective rotating gas spirals, whereby to obtain between saidworkpiece and said one wall a pair of laterally adjacent gas spiralseach of which has an axis coincident with the direction of elongation ofsaid chamber and a rotary component of movement about its respectiveaxis in direction towards the associated gas spiral.
 5. A furnace asdefined in claim 4, said burner means comprising further pairs ofburners provided in said sidewalls transversely aligned and operativefor ejecting further streams of said combustion gases at said speedsinto a further space between said workpiece and the other of said topand bottom walls whereby to provide in said further space a further pairof laterally adjacent gas spirals similar to the first-mentioned pair.6. A furnace as defined in claim 5, said guide means comprising firstand second guide instrumentalities for guiding the first-mentionedworkpiece and an additional workpiece in two vertically superposedspaced planes; and said burner means including additional pairs ofburners provided in said sidewalls transversely aligned and operativefor ejecting into the space between said workpieces two additionalsuperposed pairs of laterally adjacent gas spirals similar to thefirst-mentioned pairs of gas spirals.
 7. A furnace as defined in claim5; and further comprising divider means provided on said top and bottomwall, respectively, projecting into said chamber and extendinglongitudinally of said chamber intermediate the respective gas spiralsof each pair of gas spirals.